1. Field of Invention
This invention relates to safety devices, specifically to a mechanism for prevention of flareup in barometric-type wick-fed liquid fuel burners.
2. Discussion of Prior Art
Wick-fed liquid fuel burners, such as kerosene heaters, are used for space or area heating In cabins, mobile homes, and the like. In such burners liquid fuel from a fuel chamber is supplied to a wick which is exposed to the oxygen of the atmosphere. Once the wick has been ignited, flame intensity and heat generation are controlled by adjusting the length of the wick exposed within a wick-receiving combustion chamber.
A common type of kerosene heater is the barometric style, in which gravity causes liquid fuel to be delivered to a horizontal fuel chamber from a vertically-oriented, removable tank inserted into a mating well, or sump, in a top surface of the fuel chamber. In some cases a sight gauge is mounted on the side of the removable tank to monitor the fuel level in that tank when the tank is filled, and during operation of the burner. The flow of fuel from the removable tank into the fuel chamber is governed by a barometric valve in the cap on the removable tank, which, in normal operation, maintains the level of the fuel in the fuel chamber at the level of the barometric valve. A partial vacuum above the fuel in the removable tank prevents the fuel from flowing into the fuel chamber until the fuel level in the fuel chamber drops below the barometric valve, which allows air to enter the removable tank. As air enters the removable tank through the barometric valve, fuel in the removable tank flows into the fuel chamber until its level in the fuel chamber rises and covers the barometric valve in the removable tank cap, causing fuel flow from the removable tank to cease.
The barometric valve consists of a spring-loaded plunger, which has an enlarged head at one end. When the removable tank is inserted into the fuel chamber, the plunger head contacts a pin located in the fuel chamber, which pushes the plunger back, allowing the fuel in the removable tank to be in fluid communication with the fuel chamber.
When the tank is removed, the action of the spring on the plunger head forces it against the opening in the tank cap, sealing the opening and preventing fuel from leaving the tank. The capacity of the removable tank is typically about four to five liters (four to five quarts), while the fuel chamber can hold a maximum of about two liters (two quarts).
Various improvements have been made to such burners which make them safer to operate. For example, tip-over shut-off mechanisms, manual shut-off devices, and low-level O.sub.2 detectors have been employed. However, these burners continue to cause fires that result in death, injury, and property loss. These fires are caused, because, when high-volatility fuels are present in the burner, under certain conditions, vapors from the sump area can be ignited by the wick flame, and in other cases, fuel can overflow the fuel chamber. When the overflowing fuel ignites, the result is an uncontrolled fire, or flareup.
The most common reason for fuel overflow is the inadvertent use of fuels with high vapor pressures. Examples of such fuels are gasoline, naphtha, and inferior kerosene, which has a low flash point. In a barometric heater, overflow of fuel from the fuel chamber can occur if the partial vacuum in the removable tank is lost. As the temperature of the heater and its surroundings increases, the vapor pressure of the fuel in the removable tank increases and, under certain conditions, allows fuel to escape from the removable tank at a rate greater than the rate of wick-controlled burning of the fuel. Should this process continue, the fuel chamber will overflow, since the removable tank holds about two to three liters (two to three quarts) more than the capacity of the fuel chamber. When the fuel chamber overflows, the fuel spills onto the top of the fuel chamber, and can then ignite, causing an uncontrolled fire. A second way that the partial vacuum in the barometric heater's removable tank can be lost is by air entering the removable tank due to compromise of its integrity.
There are safety devices that drop the wick down, thereby extinguishing the flame, if the burner tips over or experiences excessive vibration, or if abnormal combustion is detected. Other safety devices detect high levels of CO.sub.2 and low levels of O.sub.2 in the vicinity of the heater, and use these to control burning rates. Still others regulate the position of the wick during the ignition and extinguishing operations of the heater to prevent excessive flaming during these operations. Examples are shown in U.S. Pat. Nos. 4,363,620, issued Dec. 14, 1982 to Nakamura; 4,872,831, issued Oct. 10, 1989 to Fujimoto; 4,797,088, issued Jan. 10, 1989 to Nakamura; and 5,165,883, issued Nov. 24, 1992 to Van Bemmel. However, not only do these devices fail to prevent flareup, they are ineffective in stopping flareup after its onset. In some cases, the safety devices require the use of electrical power and electronic circuitry for actuation: this increases the cost of the burners significantly, without rectifying the flareup problem.
It has been suggested in two publications ("Kerosene Heater Fires: Barometric Type," R. Henderson et al., Fire Marshals Bulletin (National Fire Protection Association), Vol. 87-5, p. 8 (1987); "Barometric Kerosene Heaters," R. Henderson, Fire and Arson Investigator (International Association of Arson Investigators), Vol. 39, No. 3, p. 26 (1989)) to make the size of the removable tank of barometric kerosene heaters comparable in volume to that of the fuel chamber so that flooding of the fuel chamber will not occur. To implement this suggestion, either the capacity of the removable tank must be reduced, or alternatively, that of the fuel chamber must be increased. However, reducing the capacity of the removable tank will reduce the burn time accordingly, and possibly affect the marketability of the heaters. Increasing the capacity of the fuel chamber will require that new tanks be designed and implemented and could increase the size of the burner to an unacceptable level.
Also, it has been suggested that a float device be introduced into the fuel chamber to be used to activate the automatic wick extinguishing mechanism, and a sight gauge be present to show dangerous fuel levels in the fuel chamber. Introduction of such a float device would also require that the fuel chamber be redesigned, as discussed above. Although some burners have sight gauges in the fuel chamber, the sight gauges are used only to indicate whether or not fuel is present, not when dangerous fuel levels are present in the fuel chamber.
In addition it was proposed that a tank block-out device be installed. In this, a float in the fuel chamber pushes a pin that moves if the removable tank is withdrawn from the heater. Once again, such a device would require a redesigning of the fuel chamber and insertion of moving parts inside a somewhat restricted space.
U.S. Pat. No. 5,080,578, issued Jan. 14, 1992 to Josephs, claims that its device controls flareup in wick-fed liquid fuel burners by a) cutting off the flow of fuel to the wick in response to excessive heat by blocking a fuel line, and b) withdrawing the wick into the wick chamber when sensing excessive heat. However, Josephs' device has several disadvantages:
a) Excessive heat must be gene rated near the sensors before the flow of fuel is interrupted, or the wick is withdrawn. Therefore, since flareup is not prevented, the device only limits the spread of excessive flames after flareup has al ready occurred.
b) Heat sensing devices must be near the area where uncontrolled burning is taking place due to overflow of fuel. But often the path that the overflowing fuel takes is random and flareup may not initially occur near the heat sensors.
c) The device is not applicable to barometric liquid fuel burners--one of the most common wick-fed liquid fuel burners in use--because these burners do not have fuel lines.
d) From the onset of flareup in wick-fed liquid fuel burners, fire is present outside the wick; therefore, retracting the wick does not affect the flareup process.
The device of the above U.S. Pat. No. 5,338,185 of Henderson and Lightsey consists, in part, of an excess fuel containment compartment below the level of the fuel chamber. It prevents flareup by activating a wick-extinguishing mechanism when the presence of excess fuel is detected in the fuel chamber. While this device has much merit, to be effective it requires activation of a second mechanism, that is, an automatic wick extinguisher. Should that mechanism fail to respond, due to tar buildup on the wick or a mechanical problem, flareup may still occur in some situations.
The device of the above U.S. Pat. No. 5,456,595 of Henderson prevents flareup by lifting the removable tank when excess fuel is present in the fuel chamber, thereby shutting off the barometric valve and stopping fuel flow from the removable tank. For this device to work, a spring must be provided to lift the removable tank and its contents (liquid fuel), the total weight of which can be up to some five kilograms (ten pounds). Accordingly, should the spring lose strength, or should the removable tank become hindered in its upward movements this device may not be able to prevent flareup in some situations.
The device of the above U.S. Pat. No. 5,409,370 of Henderson prevents flareup by dropping the pin which holds open the barometric valve in the removable tank cap, thereby closing the valve and stopping fuel flow into the fuel chamber. Should the valve not close properly, this device may not prevent flareup in some situations.
The device of the above U.S. Pat. No. 5,549,470 of Henderson prevents flareup by providing a thermal barrier between the combustion cylinder and the removable tank, which helps lower the temperature of the removable tank so that fuel vapor pressures do not become excessive. In addition, it includes a warning gauge that alerts the user to the dangerous condition of the burner when excess fuel is present in the fuel chamber. It also provides an excess fuel containment system that can hold the entire contents of the removable tank should all the fuel be released rapidly.
This system consists, in part, of a fuel containment sump, which extends upward from the top of the fuel chamber, and which surrounds the removable tank, but which does not have a closure at its top. This device has much merit in that it is effective without involving any moving parts for its operation. However, the presence of the components of the device would add to the weight of the burner.
The device of the above U.S. Pat. No. 5,662,468 prevents flareup by containing fumes in the vicinity of the removable tank and by providing (a) a closure at the top of the compartment housing the removable tank, and (b) a block-out mechanism for the removable tank should excess fuel be present in the fuel chamber. Although this device also has much merit, it requires the introduction of a tank block-out mechanism in the sump in a somewhat restricted space.
The device of the above U.S. Pat. No. 5,730,115, acts to prevent flareup by providing a float in the fuel chamber, which float rises in response to the presence of excess fuel in the fuel chamber. As the float rises, it moves a member which obturates an opening from the sump to the chamber, causing the opening into the fuel chamber to be closed. Should the float fail to respond, or if the opening does not seal properly, excess fuel will continue to flow into the chamber, which may result in flareup.
The device of the above U.S. Pat. No. 5,772,425, prevents flareup by containing vapors in the sump area when the removable fuel tank is inserted into the fuel chamber. A gasket contains vapors present in the sump area when the tank is seated in the sump opening. When the tank is removed from the sump opening, a plate moves upward due to the action of a spring and contains vapors in the sump area. While this device is quite effective in preventing flareup due to vapor migration from the sump area, it does not prevent flareup should excess fuel enter the fuel chamber, causing an overflow of fuel from the fuel chamber.
The device of the above U.S. Pat. No. 5,551,865 of Henderson and Henderson employs a thermocouple/solenoid/lever system, which lever must be engaged until the wick flame is established sufficiently such that the solenoid can maintain the position of the lever so that it does not actuate the automatic wick extinguishing mechanism. Should excess fuel enter the fuel chamber, a float causes the thermocouple/solenoid circuit to open, which releases the lever, actuating the wick extinguishing mechanism. This device has the advantage that there is a self-test of the system each time the burner is operated. On the other hand, the device requires electrical circuitry and components for its operation. Also, should the wick extinguishing mechanism fail to operate, flareup may result.